In a DC-DC voltage converter, the power consumption of a MOSFET is high. The source terminal or the drain terminal of the MOSFET is required to dissipate heat. Conventionally, part of a lead frame is exposed from a molding body to improve heat dissipation of the MOSFET. For example, as shown in FIG. 6 (same as FIG. 1 of the U.S. Pat. No. 8,981,539), a DC-DC converter 10 includes a HS MOSFET 11, a LS MOSFET 13, and a control chip 12. The control chip 12 outputs a pulse width modulation (PWM) or pulse frequency modulation (PFM) signal to the HS MOSFET 11 and the LS MOSFET 13 and then receives feedback signals. Electrode pads arranged on the HS MOSFET 11 and the LS MOSFET 13 are electrically connected to input/output (I/O) metal pads of the control chip 12 through a plurality of leads. The HS MOSFET 11 and the LS MOSFET 13 are respectively attached to a substrate 21 and a substrate 23. The substrate 21 and the substrate 23 are separated from each other. The source of the HS MOSFET 11 is connected to the substrate 23 through a metal sheet 15. The source of the LS MOSFET 13 is connected to the pin 24 through a metal sheet 16. The control chip 12 is attached to another separated metal substrate 22. The respective bottom surfaces of the metal substrate 21 and the metal substrate 23 are exposed from a bottom surface of a molding body of the DC-DC converter 10 (not shown). The exposed bottom surfaces are used as terminals electrically connected to external circuits for heat dissipation. The disadvantage of the DC-DC converter 10 is that dimensions of metal substrate 21 and the metal substrate 23 are large. Therefore, a device package size of the DC-DC converter 10 is large and the corresponding fabrication cost is high.
US patent application publication US20120061813A1 discloses a DC-DC voltage converter for power conversion. The DC-DC voltage converter includes a HS MOSFET and a LS MOSFET. The HS MOSFET and the LS MOSFET are arranged side by side on a substrate. A control chip is stacked on the HS MOSFET and the LS MOSFET. It requires that a metal contact lead of the HS MOSFET and the LS MOSFET must have a lower loop height to avoid the control chip to contact the metal contact lead. The heat radiating route of the HS MOSFET and the LS MOSFET is blocked by the control chip.